1. Field of Invention
The present invention relates to audio speakers and speaker systems, and in particular to an electronic circuit and method for insuring the proper operation of electronic circuits designed to protect audio speaker systems from overload.
2. Description of Related Prior Art
Electronic circuits and methods for protecting audio speaker systems from being overloaded by their input electrical signals, while maintaining substantially uniform speaker response are well-known in the art. One method by which such protection may be achieved is the use of an electronic circuit designed to protect speakers from thermal overload resulting from high frequency electrical signal current, and excessive excursion of the speaker membrane resulting from excessive low frequency electrical signal current. Circuits which prevent thermal damage to speakers by monitoring and limiting the level of input high frequency electrical signal current thereto are well-known in the art. Similarly, circuits which prevent physical damage to speakers caused by excessive excursion of their cones or diaphragms are also well-known in the art. An example of the latter and a detailed description thereof may be found in U.S. Pat. No. 4,583,245 by Gelow, et al. Such protection circuits are often referred to as audio processing systems or audio processors.
Regardless of the circuit or method used to provide such protection to a speaker, one characteristic is common to all. That is, a closed-loop system must be used. In other words, the protection circuit must monitor the actual audio signal which drives the speaker intended to be protected. This requires a feedback, or "sense," line electrically connecting the input line of the speaker and the protection circuit. Without this connection, the protection circuit cannot monitor the signal driving the speaker, leaving the speaker unprotected from potential thermal overload or physical damage.
Under normal use or operation, the requisite connection between the input of the speaker and the protection circuit is provided during the installation and setup of the audio system. However, frequently this connection will not be made due to forgetfulness or ignorance on the part of the installer, or it may fail due to some form of electrical or mechanical failure. Should this happen, the utility of the protection circuit is impaired or defeated entirely. Thus, in order to provide complete protection, the protection circuit must not only provide full protection when fully and properly connected, but it must also provide some level of protection when not fully or properly connected. Furthermore, such a fully protective circuit should provide some means of informing its installer or operator of its improper connection.